254: MORPHOLOGY AND EVOLUTION
Apes, but they are not distinctly helmet-shaped as in Man. They are composed of the usual cortex and medulla.
There is no extensive literature on the other ductless glands in the Apes—pituitary body, pineal gland, islets of Langerhans and interstitial cells of the ovary and testicle.
Section E.—THE BLOOD.
It has been shown by Gulliver (81) that there is a slow, but progressive, increase in the diameter of the red blood corpuscles in the Primates from the Lemurs up to Man; and the following list, taken from his writings, shows the measurements in the Anthropoid Apes and Man :—
Man 1/3200 inch in diameter.
Orang 1/3383 „ „
Chimpanzee 1/3412 „ ,, ,,
Gibbons 1/3549 „ „
Bio-chemical Reactions.—During the process of evolution the descendants of a common ancestor undergo modifications in structure as the result of changes in diet, the assumption of new habits or the effects of different climatic conditions. These changes may proceed so far that it is difficult to distinguish between the descendants, or to discover the common ancestor from which they have arisen. It is, therefore, obvious that any tests which will enable us to detect these descendants, in spite of the modifications in structure, will be of immense value. Such a test is present in the biochemical reactions of the blood. Professor Nuttall, who has devoted much attention to this subject, writes (369) : " This method of